This invention relates to a method and apparatus for locating or rediscovering partially obscured objects in images, by correlation of an object reference with image values.
Numerous practical uses require objects to be automatically rediscovered in images or digital image sequences. But it can happen that parts of the object are covered up or obscured by obstructions in the field of view.
In a known process for rediscovery of objects in images, the object image to be located stores a reference and that reference is subsequently correlated with the image within a limited range. Only part of the reference is used during correlation and the image pixels of that reference belong to the object. Parts that do not belong to the object are masked by object windowing or object masking. The location of the correlation maximum supplies the current position of the object in the image, because the image pixels there agree with the object pixels.
This known process however is problematic in that the correlation no longer provides the correct position of the object when it happens to be partly covered up, because one correlates in the covered area with image pixels that do not belong to the object. Due to this coverup, only part of the object is compared to the reference, which leads to an inaccurate recognition of the object or of the position of the object. Imprecise recognition of the coverage area very quickly yields an erroneous object position in the image.
It is therefore a purpose of the present invention to provide a process for rediscovering objects in images, which will facilitate precise recognition and precise determination of the object position.
Another object of the invention is to provide a system for the rediscovery of objects in images, with which the object position can be determined precisely.
These and other objects and advantages are achieved by the method and apparatus for rediscovery of objects according to the invention, which includes a correlation of an object reference with image values. If an object is partially obscured (covered up), the image values that are within the coverage area in the image, are replaced by gray values of the object or of an object reference, before the correlation is performed. In that way, the errors connected with the rediscovery of the object are significantly reduced.
As part of this process, a reference image is preferably subjected to interference windowing in order to replace the image values within an interference mask by the gray values of the object. Advantageously, the reference image is subjected to object windowing in order to get the object reference.
In the present invention, especially prior to coverup, an image of the complete object is stored, and is used to determine the position of the object in case of a partial coverup. Advantageously, covered parts of the object in the image are replaced by parts of a stored reference.
The invention-based system for the rediscovery of objects in images includes a camera to take a picture, an image data memory to store an object reference, an image data processor to replace gray values that lie in the image within a coverup area with gray values of the object reference, and a correlation unit that correlates the image—altered by the image data processor—with the object reference. The invention-based system is able precisely to recognize the coverup area and to determine a precise object position in the image. Errors are avoided or substantially reduced in that the already stored information on the appearance of the object is employed.
The invention is guided by a basic cybernetic idea: the system stores the image of the complete object and uses this information to determine what is behind the coverup. This technique is patterned after the human observer, who remembers the image of the complete object and who has an idea of what is behind the coverup. As a result, one can determine precisely the position of the object in case of partially covered objects.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.